The drive device serves, for example, for driving the motor vehicle and therefore for supplying a torque directed at driving the motor vehicle, which can also be referred to as a drive torque. For supplying the drive torque, the drive device has at least one drive assembly, such as, for example, the internal combustion engine. Obviously, the drive device can also have a plurality of drive assemblies, which preferably differ from one another, and in this respect can be designed as a hybrid drive device. In this case, for example, a first of the drive assemblies is an internal combustion engine and a second of the drive assemblies is an electric motor.
The drive device has the output shaft, at which the drive torque supplied by the at least one drive assembly, in particular the internal combustion engine, is applied. Preferably a transmission is operatively connected to the output shaft, in particular rigidly and/or permanently. By means of the clutch connected between the internal combustion engine and the output shaft, it is possible selectively either to decouple the output shaft and consequently the transmission from the internal combustion engine or to connect them operatively to the internal combustion engine. The transmission is preferably a shift transmission, by means of which different gear ratios can be adjusted, in particular a manual transmission. The clutch is, for example, a starting clutch.
It can thus be provided that the output shaft is on the side of the transmission facing away from the internal combustion engine or is a component of the transmission and is therefore in operative connection between a transmission input shaft and a transmission output shaft of the transmission. In the first case, the output shaft is, for example, a transmission output shaft. The transmission input shaft of the transmission is preferably operatively connected to the internal combustion engine, in particular rigidly and/or permanently. It can be provided that the clutch is integrated in the transmission and thus forms a component of it and in this respect is arranged in the operative connection between the transmission input shaft and the transmission output shaft. In particular, the transmission is designed as an automatic transmission or automatic shift transmission or as an automated manual transmission. The clutch is, for example, a multi-plate clutch or the like.
In order to ensure an energy-efficient operation of the motor vehicle that is as optimal as possible and correspondingly as little fuel consumption of the internal combustion engine as possible, the drive device can be operated in the so-called coasting operating mode. In this operating mode, the clutch is opened, in particular completely opened, so that the internal combustion engine is completely decoupled from the output shaft. At the same time, the idling speed control of the internal combustion engine is carried out, in which the current rotational speed of the internal combustion engine is controlled to the idling speed. The idling speed is preferably chosen to be as low as possible, but such that a further operation of the internal combustion engine is ensured and thus an inadvertent standstill is prevented. The latter may occur, for example, when the speed of the internal combustion engine drops too far below the idling speed.
The coasting operating mode is conducted, in particular when there is no torque demand, for example, by a user of the motor vehicle and/or a driver assist device. Torque demand is understood to mean a demand placed on the drive device to bring about either an acceleration or a deceleration of the motor vehicle and correspondingly to supply a drive torque that differs from zero at the output shaft. Besides the coasting operating mode, the drive device can be operated in the overrun operating mode. In this operating mode, the clutch is to be closed, preferably completely closed. At the same time, a drive torque, in particular a drive torque that is less than 0 Nm, directed at decelerating the motor vehicle, is supplied to the output shaft by means of the drive device. Such a drive torque is produced, for example, by means of friction present in the internal combustion engine and/or by corresponding actuation of gas exchange valves.
If the drive device is then operated in the coasting operating mode and a torque demand that is directed at deceleration of the motor vehicle arises, it is necessary to switch from the coasting operating mode to the overrun operating mode. To this end, for example, it is possible to adjust and, in particular, to control the speed of the internal combustion engine by means of a corresponding control to a transmission speed of the transmission. For this purpose, the amount of fuel introduced into the internal combustion engine is increased, so that the speed of the internal combustion engine, starting from the idling speed, is increased in the direction of the transmission speed. Once the internal combustion engine speed has attained the transmission speed, that is, corresponds to it, the clutch is completely closed. However, such an operating procedure is energy-consuming or necessitates an increased fuel consumption.